Pilomatricoma of the Head and Neck: A Retrospective Review of 179 Cases

Objective  To describe the clinical presentations and management of pilomatricoma, formerly known as pilomatrixoma, of the head and neck.

Design  Retrospective study.

Setting  Tertiary care center.

Patients  The study included 179 patients with a diagnosis of pilomatricoma of the head and neck.

Intervention  All patients underwent surgical excision for pilomatricoma of the head and neck between 1991 and 2002.

Results  Pilomatricoma occurred at any age (mean age, 29.8 years); 45.3% of the cases occurred in patients younger than 18 years. The female-male ratio was 0.97:1. The average size of the lesion was 1 cm. The most common sites of occurrence were the neck (30.2%), cheeks (16.8%), scalp (16.2%), and brow and periorbital area (14.0%). Multiple occurrence was found in 1 case. Two of 179 tumors recurred after surgical excision.

Conclusions  Because preoperative diagnosis of pilomatricoma is usually incorrect, careful clinical examination and a high index of suspicion would result in a more accurate diagnosis. Complete surgical excision is the treatment of choice. Otolaryngologists should consider pilomatricoma in the differential diagnosis of neck masses.

PILOMATRICOMAS, formerly known as pilomatrixomas, are superficial, benign skin tumors that are typically located in the head and neck region and most often occur before the age of 20 years. They are the second most commonly excised superficial masses in children, after epidermoid cysts and excluding lymph nodes.¹

In 1880, Malherbe and Chenantais² described calcifying epithelioma as a benign subcutaneous tumor arising from sebaceous glands. In 1922, Dubreuilh and Cazenave³ described the unique histopathologic characteristics of this neoplasm, including islands of epithelial cells and shadow cells. In 1961, Forbis and Helwig⁴ proposed the term pilomatrixoma to describe the condition to avoid a connotation of malignancy and to denote its origin from hair matrix cells.

Despite being better defined, pilomatricomas continue to be frequently misdiagnosed and are not usually considered in differential diagnoses. They typically present as a superficial, firm, solitary, slow-growing, painless mass of the dermis. The overlying skin may exhibit a bluish discoloration or ulceration. Treatment consists of surgical excision. Recurrence is rare after complete resection. Malignant pilomatricomas have rarely been reported.

Although pilomatricomas are well recognized by dermatologists and pathologists, they are relatively unknown to otolaryngologists. The objectives of this retrospective study were to analyze the data from 179 cases of pilomatricoma of the head and neck and to provide information on the clinical presentation, management, and outcome in order to better familiarize the otolaryngologist with this entity.

The records of the pathology department at Taipei Veterans General Hospital, Taipei, Taiwan, were searched for all cases of head and neck pilomatricoma between 1991 and 2002. The records of these patients were reviewed to determine sex; age at presentation; duration, location, and size of the tumor; preoperative diagnosis; treatment; pathologic features; and follow-up findings.

Of the 179 patients with the diagnosis of pilomatricoma, 88 (49.2%) were female and 91 (50.8%) were male (female-male ratio, 0.97:1). The patients ranged in age from 1 to 83 years (Figure 1); 45.3% of cases occurred in patients younger than 18 years (female-male ratio, 1.1:1). The duration from the first appearance of the mass to its initial evaluation ranged from 3 weeks to 20 years. The most common sites of occurrence were the neck (30.2%), cheeks (16.8%), scalp (16.2%), and brow and periorbital area (14.0%) (Table 1). One patient presented with multiple occurrences in the neck and forearm. The size of the surgical specimens collected ranged from 0.3 to 2 cm in 134 cases (74.7%), and the specimens were larger than 2 cm in 3 cases (1.8%). The specimen size was not specified in the histologic report in 42 cases (23.5%). The correct preoperative diagnosis was made in only 2 cases. The most common misdiagnosis was epidermoid cyst (70 cases), followed by inclusion dermoid cyst (9 cases). There were 83 cases (46.4%) without provisional diagnosis before histologic examination of the surgical specimen.

All lesions were surgically excised and 2 recurred. The diagnosis was confirmed by histopathologic examination in all cases. Histologically, the tumor consisted of enucleated shadow cells in the center and nucleated basophilic cells on the periphery (Figure 2A-D). Calcifications were present in 75 cases (Figure 2E and F). Occasional foreign body giant cells reacting to keratin debris and calcification were seen. Ossification with bone marrow formation was evident in 1 case.

Pilomatricoma, a benign neoplasm of the hair follicle, was initially thought to arise from sebaceous glands and was called calcifying epithelioma of Malherbe by Malherbe and Chenantais² in 1880. In 1961, after histochemical and electron microscopic analysis of 228 such tumors, Forbis and Helwig⁴ found the cell of origin to be the outer root sheath cell of the hair follicle and proposed the name, pilomatrixoma, now called pilomatricoma.

In 1973, Moehlenbeck⁵ reviewed 140 000 skin tumors and noted that pilomatricoma represented 0.12% of cases. Although pilomatricoma can develop in patients of any age, it occurs most often in children and young adults.^6-9 Among the young, 40% of cases occur before the age of 10 years and 60% of cases occur before the age of 20 years.^5,6,10 However, a second, smaller peak of onset has been reported in the elderly.¹⁰ In our study, 26.8% of cases occurred before the age of 10 years, 22.3% of cases occurred between the ages of 11 and 20 years, and 27.9% of cases occurred between the ages of 50 and 70 years. These numbers are in contrast to those reported in the literature that we reviewed, in which the mean percentage of patients younger than 21 years who presented with pilomatricoma was 45.4% (range, 17%-64%).⁶ The female-male ratio ranged from 0.43:1 to 2.45:1, and a female preponderance was noted in a majority of the studies.^6-11 Our study, however, did not demonstrate a female preponderance (female-male ratio, 0.97:1). One possible cause of this discrepancy may be that in the majority of the cases reported in the literature the patients were exclusively white.

The most common anatomical location for the tumor is the head and neck region; between 40% and 77% of cases occurred in this area.^6-12 The second most common site is the upper extremities, followed by the trunk and the lower extremities.^5,6,8 In the head and neck region, the most frequent locations are the neck and the frontal, temporal, periorbital, and preauricular areas.^7-9,11 In our study, the most common sites of occurrences were the neck, followed by the cheeks, scalp, and periorbital area. The neck and cheek were the most common sites in the pediatric group (age, <18 years), while the scalp and neck were the most common sites in the adult group. To our knowledge, no cases of pilomatricoma have been reported on the palms, soles, or genital region, probably because of the lack of hair-bearing skin in these areas.^8-10

Pilomatricomas are usually solitary nodules, but multiple occurrences have been observed in 2% to 10% of reported cases.^4-9 In our study, there was only 1 case of multiple pilomatricomas (neck and forearm). Multiple pilomatricomas have been associated with myotonic dystrophy, Gardner syndrome, Steinert disease, Turner syndrome, and sarcoidosis.^6,7,9,10,12

Pilomatricoma is considered to be of ectodermic origin. This theory is supported by evidence that pilomatricoma originates from the hair germinal matrix. Pilomatricoma formation represents a disturbance of the hair follicle cycle in which limited cytologic differentiation of pilar keratinocytes occurs but further development into mature hair fails to take place.¹² There is a study suggesting that apoptosis is the main mechanism leading to the development of the dead shadow cells and is most probably responsible for the banal biological behavior of pilomatricoma.¹³

The diameter of a pilomatricoma ranges from 0.5 to 3 cm in most cases.^6-11 The tumor slides freely over the underlying layer. Also, its irregular consistency, firm shape, and overlying skin discoloration are suggestive of its nature. The tumor is usually asymptomatic and grows slowly over a period of several months or years. The clinical differential diagnosis of head and neck pilomatricoma includes sebaceous cyst, ossifying hematoma, brachial remnants, preauricular sinuses, adenopathy, giant cell tumor, chondroma, dermoid cyst, degenerating fibroxanthoma, foreign body reaction, and osteoma cutis.^6-9,11,12 In the preauricular area, pilomatricomas can be particularly difficult to distinguish from tumors or inflammatory conditions that originate from the superficial lobe of the parotid gland. Although diagnosis of pilomatricoma can be based solely on the clinical features, previous reviews have shown that the accuracy rate of the preoperative diagnosis of pilomatricoma ranges from 0% to 30%.^1,7,9,10 The differences in accuracy rates may be attributable to the fact that most clinicians are not familiar with this tumor.

Radiologic imaging is of little diagnostic value for pilomatricoma.^7,8 Imaging has been used mainly for differentiating preauricular tumors from parotid tumors and for evaluating large or aggressive tumors. The characteristic computed tomographic findings are those of a sharply demarcated subcutaneous lesion with various amounts of calcification^8,9 (Figure 3). Magnetic resonance imaging has revealed high-signal bands on T2-weighted images that correlate with the bands formed by basaloid cells that are evident on histologic examination.¹⁴ Ultrasonography has also been described as a relatively fast and noninvasive method for estimating the depth of larger masses.¹¹

Histopathologic examination of pilomatricoma shows sharply demarcated dermal nodules surrounded by a capsule of compressed fibrous tissue located in the lower dermis and extending into the subcutaneous fat. The cells in the islands are arranged in a circular configuration, with nucleated basaloid cells on the periphery and enucleated shadow cells in the center (Figure 2A and B). The basaloid cells exhibit deeply staining basophilic nuclei with scant cytoplasm that lack distinct cell borders. The shadow cells, also termed ghost cells, which evolve from basaloid cells, represent dead cells that retain their cellular shape and show a central unstained area that corresponds to the lost nucleus (Figure 2C and D). The transitional cells, which are localized between basaloid cells and shadow cells, were thought to represent apoptotic cells that were finally proceeding to shadow cells. Calcification is mostly seen in the ghost cell regions, with the incidence ranging from 69% to 85%^4-6 (Figure 2E and F). Foreign body giant cell reaction, which represents a granulomatous response to the shadow cells, can also be identified in regions where keratinized debris is abundant.^8,9,12

Malignant transformation of pilomatricoma is rare, with fewer than 20 cases described in the literature.^7,8,10 Malignant pilomatricomas tend to occur in middle-aged or elderly patients. The histologic features of pilomatrix carcinoma include active proliferating basaloid cells with atypical mitoses and nuclear pleomorphism, invasion of blood vessels, and infiltration into underlying structures.^8,10 Treatment is wide local excision. Rare cases of pilomatrix carcinoma with distant metastasis have been reported.¹⁵

Fine-needle aspiration cytology has been described as a preoperative diagnostic investigation. However, the results can be misleading if there are no ghost cells present in the aspirate.^7,9 Since spontaneous regression is never observed, the standard treatment of pilomatricoma is complete surgical excision. Wide excisions with margins of 1 to 2 cm are recommended for malignant variants to minimize the risk of local recurrence.^8,9 Occasionally, the overlying skin will need to be excised because of tumor adherence to the dermis.^7,9 Recurrences after surgery are rare, with an incidence of 0% to 3%.^4,6-12 Malignant transformation to a pilomatrix carcinoma should be suspected in cases with repeated local recurrences.¹²

Pilomatricoma is a painless, firm, slow-growing, benign skin neoplasm that derives from hair follicle matrix cells. It is typically found in the neck, cheek, periorbital region, and scalp. The majority of cases occur in children and adolescents. The characteristic histopathologic appearance consists of ghost cells and basaloid cells. Recurrence after complete surgical excision is rare. The otolaryngologist should be familiar with this entity and consider it in the differential diagnosis of a superficial mass in the head and neck region.

Corresponding author and reprints: Ching-Zong Lin, MD, Department of Otolaryngology, Taipei Veterans General Hospital, 201 Shih-Pai Rd, Sector 2, Taipei 112, Taiwan (e-mail: mylan@vghtpe.gov.tw).

Submitted for publication December 3, 2002; final revision received March 7, 2003; accepted April 25, 2003.